Environ. Sci. Technol. 2006, 40, 4874-4879
Mineralogy and Characterization of Arsenic, Iron, and Lead in a Mine Waste-Derived Fertilizer AARON G. B. WILLIAMS, KIRK G. SCHECKEL,* THABET TOLAYMAT, AND CHRISTOPHER A. IMPELLITTERI Office of Research and Development, United States Environmental Protection Agency, 5995 Center Hill Avenue, Cincinnati, Ohio 45224
The solid-state speciation of arsenic (As), iron (Fe), and lead (Pb) was studied in the mine waste-derived fertilizer Ironite using X-ray absorption spectroscopy, Mo¨ ssbauer spectroscopy, and aging studies. Arsenic was primarily associated with ferrihydrite (60-70%), with the remainder found in arsenopyrite (30-40%). Lead was observed almost exclusively as anglesite (PbSO4), with 5 mg L-1 in the leaching solution). The study also estimated 37% of the As and 83% of the Pb desorbed/dissolved from the solid phase in physiologically based extraction tests meant to mimic human gastric exposure. Ironite, however, is not subject to hazardous waste restrictions because it is exempt under the Bevill Exemption, which outlines exclusions to the definitions of a hazardous waste in the Resource and Conservation Recovery Act. Under the Code of Federal Regulations 40CFR Part 261.2, solid waste from the extraction, beneficiation, and processing of ores and mineral mine wastes are excluded from the definition of a hazardous waste (4). In 2002, the EPA published a final rule on establishing regulations for zinc (Zn) fertilizers made from recycled hazardous secondary materials (5). This rule places limits on metal contaminants in these products based on Zn content. For As, the maximum allowable concentration is 0.3 mg kg-1 per 1% Zn. For Pb, the limit is 2.8 mg kg-1 per 1% Zn. At the time of the final rule for Zn fertilizers, public comments were assessed on the possibility of further regulations for fertilizers derived from mine wastes. To date, no decisions have been made on future regulations, and the impact on the sale of existing waste products is unknown. However, on the basis of values in this study, Ironite 1-0-0 to a large extent exceeds these limits (2727 mg of As kg-1 per 1% Zn and 2377 mg of Pb kg-1 per 1% Zn).. It is critical to identify the chemical speciation of contaminants to assess their risks. The objectives of this study are to (i) determine the mineralogical composition of Ironite with spectroscopic methods in an effort to accurately characterize the speciation of As and Pb and (ii) address the speciation of As and Pb in Ironite with regard to our current understanding of their stability and potential bioavailability.
Experimental Section Ironite 1-0-0 was purchased in granular form from three commercial retail stores, two in Ohio and one in Florida, and stored in its original packaging until use. To determine “environmentally available” elements (as defined in EPA method 3050B), EPA method 3051 was completed in triplicate for the three sources of Ironite. A National Institute of Standards and Technology reference, standard reference material 2711, was used for quality control. Concentrations 10.1021/es060853c Not subject to U.S. copyright. Publ. 2006 Am. Chem.Soc. Published on Web 07/13/2006
of 26 elements from the Ironite digestions were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). Matrix-matched (10%, Trace Metal Grade HNO3, Fisher Scientific, Fairlawn, NJ) ICP-AES standards were prepared from certified stock solutions. Ironite samples from the three sources were analyzed using X-ray diffraction in both crushed and granular form. Crushed samples were reduced in size to
